Phosphofructokinase in rat lung during perinatal development: characterization of subunit composition and regulation by fructose 2,6-bisphosphate and glucose 1,6-bisphosphate

Allosteric control of 6-phosphofructo-1-kinase from rat lung

1. The regulation of 6-phosphofructo-1-kinase (PFK) in the rat lung of normally fed (control), 72 hr-starved and streptozotocin-induced diabetic rats was investigated. 2. No significant changes in the total enzyme activities and the activity ratios [activity at 0.5 mM fructose 6-phosphate at pH 7.0/activity at pH 8.0 (v0.5/V)] of rat lung were observed between the control and 72 hr-starved or streptozotocin-induced diabetic rats. 3. Rat lung PFK was highly stimulated by fructose 2,6-bisphosphate (Fru-2,6-P2) as the affinity of the enzyme for fructose 6-phosphate was highly increased by this metabolite and the enzyme inhibition by ATP was released. 4. Although rat liver and mucosal PFK were found to be highly sensitive to stimulation by Fru-2,6-P2, lung PFK was significantly more sensitive to the stimulation by this metabolite than the other tissues. 5. The enzyme was highly inhibited by citrate and was only slightly inhibited by phosphocreatine. 6. ADP, AMP and c-AMP were shown to be activators of lung PFK with c-AMP being the most effective activator. 7. As a rate limiting enzyme of glycolysis, rat lung PFK is highly controlled by its allosteric effectors, especially Fru-2,6-P2, possibly for surfactant lipid synthesis which usually requires a high rate of glycolysis.

Phosphofructokinase and pyruvate kinase in mouse embryonal carcinoma P19 cells in relation to growth and differentiation

Two key enzymes of glycolysis, phosphofructokinase and pyruvate kinase, were studied in embryonal carcinoma cells (P19 EC cells) and three differentiated derivatives in relation to growth rate and differentiation state. The growth rates of P19 EC cells and its differentiated derivatives are positively correlated with both the specific activity of phosphofructokinase and the expression of the L-subunit of this enzyme. The specific activity of pyruvate kinase and its isozyme composition is not correlated with growth rate but seems to be correlated with the differentiation state of these cells. The decrease in specific activity of pyruvate kinase during differentiation of P19 EC cells induced by retinoic acid or dimethylsulfoxide preceded the shift from K- to M-type pyruvate kinase. In contrast to aggregates that were treated with dimethylsulfoxide, the specific activity of pyruvate kinase was reduced after aggregation in the presence of retinoic acid. Only after plating dimethylsulfoxide-treated aggregates again in the presence of dimethylsulfoxide, was a decrease in specific activity obtained. Both retinoic acid and dimethylsulfoxide are able to induce a K- to -M shift of pyruvate kinase.

Role of phosphofructokinase during trout haemopoiesis: physiological regulation of glycolysis

1. The regulatory properties of phosphofructokinase (PFK) has been investigated in two cellular population representatives of trout haemopoiesis; haemopoietic cells (capable of replication and differentiation) and erythrocytes (highly specialized cells). 2. The intracellular levels of substrates and effectors have been quantified and their effect on PFK activity determined. 3. Fructose 1,6-bisphosphate anc cyclic AMP show a higher activation of the PFK from haemopoietic cells than the enzyme from erythrocytes. 4. AMP and phosphoenolpyruvate act as activators of the haemopoietic cell PFK while for erythrocytes PFK, AMP is an inhibitor and phosphoenolpyruvate does not display any effect. 5. Citrate inhibits PFK activity from haemopoietic cells but was not assayed in erythrocytes since it was not detected in these cells. 6. The differences in PFK regulation in both cellular populations may be attributed to the intracellular levels of the effectors and/or different isoenzymatic patterns. 7. The different regulation of PFK together with the higher enzymatic activity of PFK and pyruvate kinase from haemopoietic cells are related to the higher glycolytic flux that exhibits the haemopoietic cells. 8. The results shown in this investigation allow us to conclude that PFK has a specific role depending on the energetic requirements of the cellular population in which the enzyme is present. 9. The requirements are related to the physiological function of each type of cell.

Phosphofructokinase in alveolar type II cells isolated from fetal and adult rat lung

The glycolytic enzyme 6-phosphofructokinase (EC 2.7.1.11) was studied in adult and fetal type II pneumocytes which had been isolated from rat lung at different days of development. In addition, the activities of the enzymes hexokinase (EC 2.7.1.1), enolase (EC 4.2.1.11) and pyruvate kinase (EC 2.7.1.40) were assayed. The specific activities of the latter enzymes decrease during perinatal development and reach about adult values shortly after birth. In contrast, 6-phosphofructokinase activity increases slightly until 2 days before birth, and drops sharply afterwards. The 6-phosphofructokinase subunit composition was determined in fetal and adult type II cells. The ratio of the three subunits of 6-phosphofructokinase in type II cells isolated on fetal days 19 and 21 (term is at day 22) and in adult type II cells was identical: the three subunits were present in a ratio of 68: 14: 18 for types L, M and C, respectively. In addition, we investigated some regulatory properties of 6-phosphofructokinase from alveolar type II cells. 6-Phosphofructokinase from alveolar type II cells is strongly inhibited by increasing MgATP concentrations. This inhibition is reflected by an increase in the S0.5 for fructose 6-phosphate. Fructose 2,6-bisphosphate stimulates alveolar type II 6-phosphofructokinase. Half-maximal stimulation occurs at 1.6 and 2.0 microM fructose 2,6-bisphosphate for fetal and adult type II cells, respectively. The level of the most potent positive effector of 6-phosphofructokinase, fructose 2,6-bisphosphate, was also determined. The level of the hexose bisphosphate decreases during prenatal development; however, the level in the adult type II cells is considerably lower. The concentration of fructose 2,6-bisphosphate appears to be sufficient to fully activate 6-phosphofructokinase both in fetal and adult type II cells.

Phosphorylation of 6-phosphofructokinase in rat lung

1. 6-Phosphofructokinase of both fetal and adult rat lung consists of L, M and C subunits in a ratio of 65:25:10. 2. 6-Phosphofructokinase was purified to homogeneity from adult rat lung and subjected to phosphorylation in vitro by the catalytic subunit of cyclic AMP-dependent protein kinase. 3. This resulted in phosphorylation of the L and M subunit of 6-phosphofructokinase. 4. The C subunit was not phosphorylated. 5. However, if the phosphorylation of 6-phosphofructokinase was studied in the cytosol fraction of either fetal or adult lung using endogenous protein kinase(s), only the L subunit was phosphorylated. 6. This phosphorylation was dependent on cyclic AMP. 7. No influence of calcium, calmodulin or phosphatidylserine/diolein on the phosphorylation was observed. 8. It is concluded that although both L and M subunits of rat lung 6-phosphofructokinase are potential substrates for cyclic AMP-dependent protein kinase, their phosphorylation in situ is differentially regulated.